Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$80.68	13.460%	$91.5395	$91.54	$91.55	$91.50
Purchase #2	$147.59	3.773%	$153.1586	$153.16	$153.15	$153.20
Purchase #3	$33.27	12.747%	$37.5109	$37.51	$37.50	$37.50
Purchase #4	$51.37	11.585%	$57.3212	$57.32	$57.30	$57.30
Purchase #5	$66.28	4.620%	$69.3421	$69.34	$69.35	$69.30
Purchase #6	$178.93	9.377%	$195.7083	$195.71	$195.70	$195.70
Purchase #7	$72.48	4.688%	$75.8779	$75.88	$75.90	$75.90
7 purchase totals =	$630.60		$680.4585	$680.46	$680.45	$680.40